Medical Definition of Myostatin

Myostatin: A growth factor that regulates the size of muscles beginning in early embryonic development and continuing throughout life. Myostatin acts by inhibiting the growth of muscles, It prevents them from growing too large. Myostatin is also known as growth and differentiation factor 8 (GDF-8). It is a protein made up of two identical subunits. Each subunit contains 110 amino acids. The gene encoding myostatin is termed MSTN (or GDF8) and is on chromosome 2 in band 2q32.1.

Myostatin is a member of the transforming growth factor beta (TGF-beta) family. All of the members of this gene family regulate growth and differentiation from early embryogenesis to mature cell types and tissues.

Myostatin was first found to regulate muscle mass in mice from which the gene encoding myostatin had been knocked out (deleted). In these "mighty mice," there is muscle overgrowth due to an increase both in the number of myocytes (muscle cells) and the size (hypertrophy) of the myofibers (muscle fibers). Breeds of cattle with exceptional muscle development -- referred to as "double-muscled" cattle -- have a mutation in the bovine MSTN gene encoding myostatin.

A child born with very large muscles was discovered to have mutation of the MSTN gene encoding myostatin, providing very strong evidence that myostatin is a lead actor in regulating muscle mass in humans. Aside from the increase in the size of his muscles, the child appeared normal at age 4. The child has a loss-of-function mutation in the MSTN gene that inactivates myostatin It may be possible to increase muscle mass and strength by inactivating myostatin in people with muscle wasting due to disease (Schuelke M et al. New Engl J Med 350:2682,2004).